Lymphosarcoma in children represents about 10 per cent of the malignant neoplasms found in the pediatric age group. It is found more often in males and seldom under 1 year of age. Classification is difficult, but most lesions can be classified as lymphoblastic, lymphocytic, or reticulum cell sarcomas. Conversion of lymphosarcoma to leukemia is frequent (one-third to one-half of reported cases) and survival is low. Cures are reported, however. The initial sites of involvement determined clinically and defined roentgenographically are not necessarily identical, but both suggest that the most frequent sites of primary involvement are the mediastinum, gastrointestinal tract, retroperitoneum and lymph nodes (diffusely). Initial roentgenographic findings may be considered as occurring very frequently, frequently, or infrequently (occasionally).